Current transfer in homopolar machines

ABSTRACT

Current transfer in a homopolar dynamo-electric machine is effected by liquid metal which is caused to flow from the periphery of the rotor by centrifugal action and impinges on a stationary trough which provides a current transfer surface and serves to collect the liquid metal, which can then be recirculated to the rotor. The liquid metal can emerge from a porous pad to engage with brushes in the trough but in a preferred construction is sprayed from annular distribution trough which projects from the periphery of the rotor into the collecting trough.

United States Patent McNab 145-1 Aug. 1, 1972 [54] CURRENT TRANSFER IN 2,828,431 3/1958 Klaudy ..310/178 HOMOPOLAR MACHINES 3,546,508 12/1970 Harvey ..310/178 2 786155 3/1957 Sellers ..310/219 F E [72] g g McNab 2,832,909 4/1958 Bnll ..310/219 g 3,211,936 10/1965 Harvey ..310/178 [73] Assignee: International Research 8: Developmem cmpany Llmlted, Fosswayi Primary Examiner-J. D. Miller England Assistant Examiner-R. Skudy [22] Filed; 19 19 70 Attorney-Kemon, Palmer & Estabrook Current transfer in a homopolar dynamo-electric [30] Forms" Apphcalon Pnomy Data machine is effected by liquid metal which is caused to Aug. 27, 1969 England ..42,638/69 flow from the periphery of the rotor by centrifugal ac.

, tion and impinges on a stationary trough which pro- U.S. v yides a current transfer urface and serves to collect Int. Cl. the metal which can then be re circulated to Field 0f Search "310/1731 the rotor. The liquid metal can emerge from a porous 310/268 pad to engage with brushes in the trough but in a preferred construction is sprayed from annular dis- [56] References C'ted tribution trough which projects from the periphery of UNITED STATES PATENTS the rotor into the collecting trough.

3,191,082 6/1962 Csillag ..310/219 7 Claims, 9 Drawing Figures M \i m 11 O CURRENT TRANSFER IN HOMOPOLAR MACHINES This invention relates to current transfer means for homopolar electro-dynamic machines.

One of the factors limiting the power density obtained from homopolar machines is the method by which current is transferred from moving to static surfaces. Most conventional machines employ 'solid copper/carbon brushes which generally limit the surface speeds to about 10,000 ft per minute and current densities to about 200 amp/sq.in. This limits the angular speed of the rotor and thus limits the voltage generated. A high power output therefore necessitates a high current density and a large contact surface. In general, machines of this nature employing solid brushes are limited to outputs of about 30,000 amps and volts at 3,000 rpm. and, although larger diameter machines operating at lower speeds would permit an increase in output, they are mainly impracticable.

Many ways of overcoming difficulties in current collection are known, involving the use of liquid metals e.g., sodium, sodium/potassium alloy, mercury, mercury amalgams and other low melting point alloys. These methods entail the interposing of liquid metal between the rotor and the means for current collection and include methods involving discreet or sheet jets of liquid metal directed onto the rotor surface from a stationary nozzle and may also involve the use of porous metal pads through which the liquid metal is pumped.

According to the present invention there is provided a homopolar dynamo-electric machine having current transfer means comprising a stationary current collection surface or surfaces surrounding the periphery of the rotor, an opening or openings at the periphery of the rotor, and means for introducing liquid metal to a region radially inwards of the periphery of the rotor which communicates with the said opening or openings so that upon rotation of the rotor the action of centrifugal force will create a substantially radial pressure head in the liquid metal and cause it to issue through the said opening or openings to impinge upon the current collection surface or surfaces.

, In one embodiment the rotor comprises a simple double or multiple tube arrangement with jets having a circular cross-section.

In a further embodiment the liquid metal issues from a substantially continuous circumferential slot. formed in the outer periphery of the rotor to produce a sheet jet of liquid. I

In a further embodiment the liquid metal flows through passages or discreet or sheet jets onto a continuous porous ring or a series of porous pads located on the outer periphery of the rotor.

In a further embodiment a pumping system is employed which utilizes the rotation of the rotor to pump the liquid metal into the inner region of the rotor.

In yet another embodiment the rotor has an annular distribution trough around its periphery which is open on its radially inward side to allow for the introduction of the liquid metal from a stationary supply pipe or pipes and has the opening or openings formed in its radially outward side. The distribution trough can lie within a collecting trough one of whose surfaces forms the current collection surface and the liquid metal can be pumped from the collecting trough back to the supply pipe or pipes.

The rotor can be constructed of electrically insulating material and the liquid metal will then serve as the rotor conductors in which the current is generated. Preferably however the rotor is electrically conducting and the liquid metal serves primarily for current transfer at the periphery of the rotor.

The invention will now be described in more detail with reference to the accompanying drawings, in which:

FIG. 1 is an end elevation of a homopolar generator in accordance with the invention;

FIG. 2 is a section on I-I of the embodiment shown in FIG. 1;

FIG. 3 is an elevation of a further embodiment of the invention;

FIG. 4 is a section on I--I of the embodiment shown on FIG. 3; 4 FIG. 5 shows an alternative configuration of the peripheral slot shown in FIG. 4 on a larger scale;

FIG. 6 is an elevation of a further embodiment of the invention with part cut away;

FIG. 7 is a section on I-I of the embodiment shown in FIG. 6;

FIG. 8 is a section of a complete machine showing a further feature; and I FIG. 9 is a partial cross-section of a further embodiment of the invention.

FIGS. 1 and 2 show the rotor assembly and current collection arrangement for a homopolar generator. For simplicity the field coils and stator are not shown. I The rotor comprises a composite hollow hub 11 and shaft 12 which are journalled between bearings 13. Two tubes 14 and 15 are securely attached to the hub and are fitted with conical nozzles 16 and 17. A stationary circumferential trough I8 surrounds and is spaced away from the tubes 14 and 15. The trough 18 has a deflecting inner surface 19 leading to the inside of the trough. The trough 18 also forms one current collecting member the other being a conventional brush sliding on the surface of the rotor shaft 12.

The hollow shaft 12 and hub 11 of the rotor are filled with liquid metal by any form of low pressure pump (not shown).

In operation the rotor is driven by mechanical means to rotate and cut the lines of force produced by stationary field windings, not shown, located on both sides of the rotating tubes. In accordance with a well known principle a d.c. current is produced and will be transferred to the trough 18 through the liquid metal issuing at high velocity from the conical nozzles 16 and 17 of the rotor. The liquid metal impinges upon the collector trough 18, being then deflected into the interior of the trough by the inner surface 19. The excess liquid falls to the bottom of the trough and is Pumped back into the interior of the rotor by the low pressure pump.

FIGS. 3 and 4 show a further embodiment in which the rotor is formed in two halves 20 and 21, joined together by internal webs to form a hollow interior I through which the liquid metal passes. The outer periphery of the rotor has a continuous gap or slot 22 around its circumference from which will issue a continuous sheet jet of high velocity liquid metal in the same manner as described above.

FIG. 5 shows an alternative form of the slot nozzle 22 formed by the rotor halves 20 and 21 by means of which the velocity of the sheet jet may be increased.

In this embodiment a series of conventional brushes 26 are used to collect current from the rotor. The brushes 26 are fixed to the inside of a continuous stationary collecting trough 27 which surrounds the rotor and shaft-assembly.

FIG. 8 shows a further embodiment having a closed cycle pumping system for pumping the liquid metal from a reservoir 28 sealed to the end of the shaft 12 by rotary seals 29. The reservoir 28 is of circular crosssection and has a plain central spigot 30 on which the shaft 12 rotates. The inside of the shaft 12 is formed with an Archimedean spiral 31 which pumps the liquid metal from the reservoir into the interior of the rotor. The collector trough 18 is connected by a conduit 32 to return the liquid metal to the reservoir. It will however be necessary to introduce some form of isolator into the connection between the trough 18 and the reservoir 28 to prevent short circuiting of -the machine. This could take the form of a mesh grating which will break the liquid metal into droplets, thus presenting a discontinuity in the current path.

In the embodiment of FIG. 9 the periphery of a rotor 33 carries an annular trough 34 which is open on its radially inward side towards the axis 35 about which the rotor rotates. A stationary supply or inlet pipe 36 feeds liquid metal to the trough and this liquid metal emerges from openings 37 to impinge on a current collection surface 38 formingpart of an annular trough 39 which surrounds the distribution trough 34 and serves to collect the liquid metal which is then returned by a pump 40 to the inlet pipe 36. In a modification of this construction the trough 34 is disposed in a recess in the periphery of the rotor and the collecting trough 39 can be similar to the trough 18 used in other embodiments.

Further embodiments of this invention may comprise combinations of features of the embodiments described. Also the embodiment described in FIG. 1,

may comprise more than two tubes, or the rotor may be a solid disc having a series of radial passages to allow the liquid metal to flow from the interior of the rotor to the outer periphery.

I claim: 1. In a homopolar dynamo-electric machine, current transfer means comprising stationary brush means arranged around the periphery of the rotor, at least. one

opening in the rotor at the periphery thereof,'a porous pad covering said opening, means for introducing liquid metal to the rotor in a region radially inwards of the periphery, at least one rotor passage connecting brgshxie agg f oggn ngg art of said trou wherein the rotor has an annular distribution trough open on its radially inward side, said opening being formed in the radially outward side of said distribution trough and said means for introducing liquid metal comprising at least one stationary supply pipe feeding into the radially inward side of said trough.

4. A homopolar machine as claimed in claim 3 having an annular collection trough surrounding the periphery of the rotor to receive said liquid metal, the current collection surface forming part of said collection trough.

5. A homopolar machine as claimed in claim 4 in which the distribution trough is located within the collection trough.

6. A homopolar machine as claimed in claim 5 having a pump for drawing liquid metal from the collection trough and feeding it to the supply pipe.

7. A homopolar machine as claimed in claim I in which the said region into which liquid metal is introduced is a central region of the rotor and the rotor is formed to act as a pump for pumping the liquid metal to the said central region.

h. achme as clafmed in claim 1 

1. In a homopolar dynamo-electric machine, current transfer means comprising stationary brush means arranged around the periphery of the rotor, at least one opening in the rotor at the periphery thereof, a porous pad covering said opening, means for introducing liquid metal to the rotor in a region radially inwards of the periphery, at least one rotor passage connecting said region to said opening, whereby upon rotation of the rotor, the liquid metal is caused by centrifugal forces to flow generally radially through the passage and issue through said porous pad to contact said stationary brush means.
 2. Current transfer means as claimed in claim 1 comprising an annular trough surrounding the periphery of the rotor for the collection of the liquid metal, said brush means forming part of said trough.
 3. A homopolar machine as claimed in claim 1 wherein the rotor has an annular distribution trough open on its radially inward side, said opening being formed in the radially outward side of said distribution trough and said means for introducing liquid metal comprising at least one stationary supply pipe feeding into the radially inward side of said trough.
 4. A homopolar machine as claimed in claim 3 having an annular collection trough surrounding the periphery of the rotor to receive said liquid metal, the current collection surface forming part of said collection trough.
 5. A homopolar machine as claimed in claim 4 in which the distribution trough is located within the collection trough.
 6. A homopolar machine as claimed in claim 5 having a pump for drawing liquid metal from the collection trough and feeding it to the supply pipe.
 7. A homopolar machine as claimed in claim 1 in which the said region into which liquid metal is introduced is a central region of the rotor and The rotor is formed to act as a pump for pumping the liquid metal to the said central region. 